Yttria-stabilized Zirconia Films Research Articles

Elaboration of Yttria-Stabilized Zirconia Films on Porous Substrates

The development of solid oxide fuel cell has shown that the thin film concept for the electrode supported designs, based on the yttria-stabilized zirconia, is more promising than the research of new electrolyte materials. In this work, the spray pyrolysis process was investigated in order to obtain dense thin films of YSZ on porous ceramic substrates. High porosity LSM, a typical material of SOFC cathodes, was used as substrate. The precursor solution was obtained by zirconium and yttrium salts dissolved in a mixture of ethanol and propylene glycol, with volume ratio 1:1. The substrate was heated and maintained at a constant temperature (280°C, 340°C or 560°C). The as-obtained films were heat treated in a temperature of 700°C, aiming to obtain yttria-stabilized-zirconia films from the amorphous film. The morphology and microstructure of the films were characterized by scanning electron microscopy and X-ray diffraction.

Microstructural factors of electrodes affecting the performance of anode-supported thin film yttria-stabilized zirconia electrolyte (∼1 μm) solid oxide fuel cells

The effects of the microstructural factors of electrodes, such as the porosity and pore size of anode supports and the thickness of cathodes, on the performance of an anode-supported thin film solid oxide fuel cell (TF-SOFC) are investigated. The performance of the TF-SOFC with a 1 μm-thick yttria-stabilized zirconia (YSZ) electrolyte is significantly improved by employing anode supports with increased porosity and pore size. The maximum power density of the TF-SOFCs increases from 370 mW cm −2 to 624 mW cm −2 and then to over 900 mW cm −2 at 600 °C with increasing gas transport at the anode support. Thicker cathodes also improve cell performance by increasing the active reaction sites. The maximum power density of the cell increases from 624 mW cm −2 to over 830 mW cm −2 at 600 °C by changing the thickness of the lanthanum strontium cobaltite (LSC) cathode from 1 to 2–3 μm.

Evidence of Proton Transport in Atomic Layer Deposited Yttria-Stabilized Zirconia Films

This study presents spectroscopic and electrochemical evidence that verifies proton transport in the temperature regime 300−450 °C in yttria-stabilized zirconia (YSZ) thin film membranes fabricated by atomic layer deposition (ALD). High-resolution X-ray photoelectron spectrometry (XPS) of O1s showed that the OH peak was significantly more pronounced in ALD samples than in single-crystal YSZ. Similarly, secondary ion mass spectrometry (SIMS) measurements, conducted for comparison on single-crystalline YSZ and atomic layer deposited YSZ, indicated that ALD YSZ contains 100 times higher deuterium concentration than single crystalline YSZ. SIMS depth profiles suggested diffusion of protons through protonic defects in YSZ. We have also fabricated fuel cells employing ALD YSZ with dense palladium layers to block oxygen but allow hydrogen transport. These performed as protonic fuel cells at intermediate temperatures achieving 10 mW/cm2 at 450 °C. These results open the possibility to engineer ALD YSZ as electrol...

Epitaxial growth of YSZ buffer layer for YBa 2Cu 3O 7− δ coated conductor by reel-to-reel pulsed laser deposition

Yttria-stabilized zirconia (YSZ) buffer layers were deposited on CeO 2 buffered biaxially textured Ni–W substrate by reel-to-reel pulsed laser deposition (PLD) for the application of YBa 2Cu 3O 7− δ (YBCO) coated conductor and the influence of substrate temperature and laser energy on their crystallinity and microstructure were studied. YSZ thin films were prepared with substrate temperature ranging from 600 to 800 °C and laser energy ranging from 120 to 350 mJ. X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate how thin film structure and surface morphology depend on these parameters. It was found that the YSZ films grown at substrate temperature below 600 °C or laser energy above 300 mJ showed amorphous phase, the (0 0 1) preferred orientation and the crystallinity of the YSZ films were improved with increasing the temperature, but the surface roughness increased simultaneously, the SEM images of YSZ films on CeO 2/NiW tapes showed surface morphologies without micro-cracks. Based on these results, we developed the epitaxial PLD-YSZ buffer layer process at the tape transfer speed of 3–4 m/h by the reel-to-reel system for 100 m class long YBCO tapes.

Yttria-stabilized zirconia thin film electrolyte produced by RF sputtering for solid oxide fuel cell applications

Thin film (40–600 nm) yttria-stabilized zirconia (YSZ) electrolytes for solid oxide fuel cells (SOFC) were deposited on NiO-YSZ anodes and fused silica substrates by RF sputtering, using low applied power without the use of post deposition annealing heat treatment. YSZ film showed a nanocrystalline structure and consisted of the Zr .85Y .15O 1.93 (fcc) phase. The film was dense and the YSZ/anode interface was continuous and crack free. According to preliminary in-plane conductivity measurements (temperature range 550–750 °C) on the YSZ film, the activation energy for ionic conduction was found to be 1.18 ± 0.01 eV.

Picosecond pulse laser ablation of yttria-stabilized zirconia from kilohertz to megahertz repetition rates

Thin films of yttria stabilized zirconia were deposited onto silicon substrates using high repetition rate picosecond pulse lasers. The applied lasers covered the repetition rate range from 10 kHz to 4 MHz. We found that the laser pulse overlapping which results from increased repetition rates led to considerable changes in the ablation process. Defect formation and local heating lead to lower ablation thresholds and, with sufficiently high repetition rates, to melting of the target and even to thermal evaporation. We found that yttria-stabilized zirconia (YSZ) films deposited with picosecond pulses at 1064 nm wavelength below repetition rates of 2 MHz have rough, nanostructured morphology and the same atomic ratio of yttrium and zirconium as the target. Films deposited with 2 MHz and higher repetition rates with high number of overlapping pulses are very smooth, but are yttrium deficient, providing evidence of the importance of the thermal processes.

Yttria stabilized zirconia solid electrolyte surface modification with ZrO2, Y2O3, and ZrO2 + 9 mol % Y2O3 films

The surface of ceramic electrolyte ZrO2 + 9 mol % Y2O3, hereinafter referred to as YSZ (abbreviated yttria stabilized zirconia), was modified with 0.1 to 0.2 μm oxide films of ZrO2, Y2O3, and YSZ (same composition as substrate) by dip coating in alcohol solutions of the relevant salts and further annealing. The results of scanning electronic microscopy and X-ray diffraction evidence epitaxial film growth. By means of impedance spectroscopy at the temperatures of 500 to 600°C, the effect of YZS electrolyte surface modification with ZrO2, Y2O3, and YSZ films to the polarization resistance of silver electrode was studied.

Effects of dopant concentration and impurities on the conductivity of magnetron-sputtered nanocrystalline yttria-stabilized zirconia

Cubic yttria-stabilized zirconia (YSZ) films with yttria concentrations of 8.7, 9.9, and 11 mol% have been deposited by reactive pulsed DC magnetron from Zr–Y alloy targets. The overall microstructure and texture in the films showed no dependence on the yttria concentration. Films deposited at floating potential had a < 111> texture. Single-line profile analysis of the 111 X-ray diffraction peak yielded a grain size of ∼ 18 nm and a microstrain of ∼ 2%, regardless of deposition temperature. Films deposited at 400 °C and selected bias voltages in the range from − 70 V to − 200 V showed a reduced grain size for higher bias voltages, yielding a grain size of ∼ 7 nm and a microstrain of ∼ 2.5% at a bias voltage of − 200 V with additional incorporation of argon. Furthermore, the effect of impurities on the ionic conductivity has been investigated, since Hf impurities were found in the samples with yttria concentrations of 8.7, and 9.9 mol%. Temperature-dependent impedance spectroscopy of the YSZ films, deposited at 400 °C and floating potential, showed no variation of the in-plane ionic conductivity with yttria concentration. However, for films deposited at 400 °C and a bias − 70 V, the in-plane ionic conductivity decreased systematically for samples with yttria concentrations of 8.7 and 9.9 mol% compared to the sample with 11 mol% yttria. This suggests that ionic conduction is not a purely bulk mechanism, but mainly related to the grain boundaries. The activation energy for oxygen ion migration was determined to be between 1.25 and 1.32 eV.

Improvement of plasma-sprayed YSZ electrolytes for solid oxide fuel cells by alumina addition

Atmospheric plasma spray is a fast and economical process for deposition of yttria-stabilized zirconia (YSZ) electrolyte for solid oxide fuel cells. YSZ powders have been used to prepare plasma-sprayed thin ceramic films on the metallic substrate employing plasma spray technology at atmospheric pressure. Alumina doping was employed to improve the structural characteristics and electrical properties of YSZ. The effect of alumina addition from 1 to 5 wt.% on the properties of plasma-sprayed YSZ films was investigated. It was found that the gas permeability of the Al-doped YSZ electrolyte layer reached a level of 8.6 × 10−7 cm4 gf−1 s−1, which is a necessary value for the practical operation of solid oxide fuel cells. Alumina doping considerably increased the ionic conductivity of plasma-sprayed YSZ. The open circuit voltage of the alumina-doped YSZ coating was approximately equal to the theoretical value for dense YSZ material.

Electrical characterization of thermomechanically stable YSZ membranes for micro solid oxide fuel cells applications

Yttria-stabilized zirconia free-standing membranes were fabricated by pulsed laser deposition on Si/SiO 2/Si 3N 4 structures for developing silicon-based micro devices for micro solid oxide fuel cell applications. Their mechanical stability under working conditions was evaluated satisfactorily by applying thermal cycling to the membranes. Membranes mechanically stable at operating temperatures as high as 700 °C were obtained for deposition temperatures in the range between 400 and 700 °C. Thermomechanical behavior as measured by X-ray microdiffraction was correlated with the evolution of the microstructure with the temperature from TEM analysis, comparing as-deposited and post-deposition annealed membranes. Electrical properties of both yttria-stabilized zirconia films and membranes were studied by DC conductivity and impedance spectroscopy, respectively. A difference of almost one order of magnitude was measured between bulk and stressed films while conductivities close to the bulk were observed for YSZ membranes. Values of area specific resistance of 0.15 Ωcm 2 were measured at temperatures below 450 °C for 240 nm thick YSZ membranes deposited at 600 °C and annealed at the same temperature for 2.5 h.

Relationship between radiation damage anisotropy in MgO and YSZ single crystals and the Ion/Atom ratio deposition parameter in biaxially-textured MgO and YSZ thin films fabricated by ion beam assisted deposition

To elucidate the underlying physics of ion beam assisted deposition (IBAD), irradiation damage effects in magnesia (MgO) and yttria-stabilized zirconia (YSZ) were investigated. Ion irradiations were performed on MgO and YSZ single crystals of three low-index crystallographic orientations using 100 and 150 keV Ar + ions over a fluence range from 1 × 10 14 to 5 × 10 16 Ar/cm 2. Damage accumulation was analyzed using Rutherford backscattering spectrometry combined with ion channeling. Damage evolution with increasing ion fluence proceeded via several characteristic stages and the total damage exhibited a strong dependence on crystallographic orientation. For both MgO and YSZ, damage anisotropy was maximal at a stage when the damage saturated, with the (1 1 0) crystallographic orientation being the most radiation damage resistant. The Ion/Atom ratio deposition parameter reported for IBAD of MgO and YSZ films was found to correlate with the damage plateau stage described above. Finally, the role of the Ion/Atom ratio is discussed in terms of radiation damage anisotropy mechanism.

Silicon-based Micro Platforms for Characterization of Nanostructured Layers With Application in Intermediate Temperature Micro Solid Oxide Fuel Cells

AbstractThe present work is devoted to study the development of yttria-stabilized zirconia membranes self-supported on silicon-based microplatforms, to be used as electrolytes on micro solid oxide fuel cells. The microfabrication process to obtain yttria-stabilized zirconia membranes is detailed, and some key aspects for the integration of yttria-stabilized zirconia films deposited by pulsed laser deposition on the silicon-based microplatform are shown. Moreover, the effect on the thermomechanical stability of different fabrication parameters is presented, as well as the way to control the pinhole generation on the membranes. Finally, some electrical characterization guidelines are included, in order to study the effects of the platform and the membrane dimensions on the different measurements performed.

Nanoporous YSZ film in electrolyte membrane of Micro-Solid Oxide Fuel Cell

Yttria stabilized zirconia (YSZ) with 8 mol% Y was deposited by reactive magnetron sputtering onto oxidized (100) silicon substrates. It was possible to switch film texture from (111) to (200) by applying a strong RF substrate bias. Transmission electron microscopy showed that the film deposited under bias is porous and exhibits nanoscaled grains, whereas the film deposited without bias is dense and columnar. The ionic conductivity as a function of temperature revealed an activation energy of 1.04 eV. The mechanical stress could be tuned to low values by thermal post-annealing. Using the dense (111) film as electrolyte layer, and the porous (200) film as an interlayer to a porous Pt anode, an open circuit voltage of 0.85 V was obtained in a micro machined fuel cell structure.

The growth-temperature-dependent interface structure of yttria-stabilized zirconia thinfilms grown on Si substrates

We report on the interface characteristics of yttria-stabilized zirconia films grown on siliconsubstrates. From x-ray reflectivity analysis we found that the film thickness and interfaceroughness decreased as the growth temperature increased, indicating that the growthmechanism varies and the chemical reaction is limited to the interface as the growthcondition varies. Furthermore, the packing density of the film increased as the growthtemperature increased and the film thickness decreased. X-ray photoelectron spectroscopyanalysis of very thin films revealed that the amount of chemical shift increased as thegrowth temperature increased. Intriguingly, the direction of the chemical shift ofZr was opposite to that of Si due to the second nearest neighbor interaction.

Oxidation behavior of ferritic steel alloy coated with LSM–YSZ composite ceramics by aerosol deposition

Composite ceramic thick film of lanthanum strontium manganate (LSM) and yttria-stabilized zirconia (YSZ), 2–6 μm in thickness, were deposited on ferritic stainless steel (STS444) by aerosol deposition (AD), as an oxidation resistance coating layer in the metallic interconnector of a solid oxide fuel cell (SOFC). The YSZ volume ratio in the LSM–YSZ composite layer was adjusted from 0 to 100 vol% and the electrical resistivity was measured at 800 °C using a DC 4-probe method. The interface microstructure and composition of the coating layer and stainless steel after oxidation at 800 °C in air was examined. The coated oxide layers were highly dense without pores or cracks and maintained good adhesion, even after oxidation at 800 °C for 250 h at all compositions. The LSM–YSZ composite ceramics showed higher stability and electrical conductivity than the sole LSM layer at 800 °C, possibly due to the high microstructural stability of YSZ against grain growth at 800 °C.

Low Temperature Performance Improvement of SOFC with Thin Film Electrolyte and Electrodes Fabricated by Pulsed Laser Deposition

The performance of solid oxide fuel cells (SOFCs) with thin film electrolytes and electrodes was investigated at a lower operating temperature regime . anode-supported unit cells with thin film components of a Ni–yttria-stabilized zirconia (YSZ) composite anode interlayer, a thin YSZ electrolyte, and a lanthanum strontium cobalt oxide cathode were fabricated by using pulsed laser deposition, and the performance of the cells was characterized at the temperature range of . Stable open-circuit voltage values above 1 V were successfully obtained with thin film electrolyte cells, which implied that the thick electrolyte was fairly dense and gastight. The thin film electrolyte cells exhibited a much more improved cell performance than a thick film YSZ electrolyte cell at the low operating temperature regime and, in some cases, showed better power outputs than other thin film membrane micro-SOFCs.

In-Plane Conductivities of Atomic Layer Deposited Yttria-Stabilized Zirconia Electrolytes for Solid Oxide Fuel Cells

We investigated oxide ion conductivities of ultra-thin (8 nm - 55 nm) yttria-stabilized zirconia (YSZ) films produced by atomic layer deposition (ALD). In-plane oxide ion conductivities were measured as a function of film thickness, temperature, and yttria concentration in the film. We observed higher conductivities for thinner films due to the portion of oxide ion conduction along the surface increased. We also observed changes in conductivities by modifying yttria concentrations near the surfaces, and the optimal concentration near the surface was different from the bulk.

Surface Modification of Yttria-Stabilized Zirconia Electrolyte by Atomic Layer Deposition

Yttria-stabilized zirconia (YSZ) electrolyte membranes were surface modified by adding a 1 nm thin, high-yttria concentration YSZ film with the help of atomic layer deposition. The addition of the 1 nm film led to an increase of the maximum power density of a low-temperature solid oxide fuel cell (LT-SOFC) by a factor of 1.50 at 400 degrees C. The enhanced performance can be attributed to an increased oxide ion incorporation rate on the surface of the modified electrolyte.

Performance of cone-shaped tubular anode-supported segmented-in-series solid oxide fuel cell stack fabricated by dip coating technique

A simple and feasible technique is developed successfully to fabricate the cone-shaped tubular segmented-in-series solid oxide fuel cell (SOFC) stack. The cone-shaped tubular anode substrates and yttria-stabilized zirconia (YSZ) electrolyte films are fabricated by dip coating technique. After sintering at 1400 °C for 4 h, a dense and crack-free YSZ film with a thickness of about 35.9 μm is successfully obtained. The single cell, NiO–YSZ/YSZ/LSM–YSZ, provides a maximum power density of 1.08 and 1.35 W cm−2 at 800 and 850 °C, respectively, using moist hydrogen (75 ml/min) as fuel and ambient air as oxidant. A two-cell-stack based on the above-mentioned cone-shaped tubular anode-supported SOFC was assembled and tested. The maximum total power at 800 °C was about 3.7 W.

Correlation between yttria stabilized zirconia particle size and morphological properties of NiO–YSZ films prepared by spray coating process

A systematic approach was taken to investigate the morphology of NiO–yttria stabilized zirconia (YSZ) films deposited by a spray coating process. The final morphological aspects of anode films were influenced by the particle size of YSZ powders and the milling time of the slurries used for film deposition. YSZ powders with average particle size of 17 and 52 nm were obtained from powders calcined at 800 and 1000 °C, respectively. The results obtained by rheological studies pointed out that slurries prepared from YSZ powders calcinated at 1000 °C and milling time of 20 h had more stability. All slurries presented thixotropic and pseudoplastic behaviors.